Escherichia coli patterns
When E. coli cells, chemotactic towards aspartate, are inoculated in a soft agar plate (0.2-0.3%) containing intermediates of the tricarboxylic acid cycle (e.g. fumarate or succinate), the cells move outward in a compact ring that eventually breaks up into spots. As the ring continues to expand, new spots form. Depending upon the concentration of the carbon source, they are in-line radially, hexagonally arrayed, or hexagonally arrayed with radial tails.
The movie starts about 3 h after inoculation soon after the first set of spots have appeared and continues for another 10 h. Note that cells leave one set of spots and move radially to rejoin the ring before the next set of spots form.
When the experiment is done in a liquid medium containing methylcellulose to suppress convection, beginning with cells that are uniformly distributed and then adding the carbon source, discrete aggregates form.
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